chore(deps): bump span-panel-api to 2.6.2

[cayossarian]

Summary

• Bumps span-panel-api dependency from 2.6.1 to 2.6.2 in manifest.json, pyproject.toml, and uv.lock.
• Picks up the MQTT reconnect loop log-noise fix (fix(mqtt): split reconnect loop handler to reduce log noise span-panel-api#137): offline-panel reconnect failures now log a one-line WARNING with the exception repr instead of a full paho/stdlib traceback; unexpected exceptions still include exc_info=True for support-ticket triage.
• Updates the 2.1.0-unreleased CHANGELOG entry to reference v2.6.2 instead of v2.6.1 in the panel-offline bullet.

Test plan

• Integration loads against a live panel (no manifest-resolution errors on startup)
• Take panel offline — confirm the log shows a single-line WARNING (Reconnect failed (ConnectionRefusedError(61, 'Connection refused')), retrying in 60.0s) with no paho/stdlib stack frames
• Bring panel back online — confirm the grace period logic and reconnect behavior are unchanged